How long could you go without eating before you'd be too weak to even hunt or forage?

I was wandering around on the internets and found this article, called, “11 survival tips which could kill you.” I thought the following was interesting:

Myth – You must find a food source immediately.

So the television screen comes to life and we see our adventure hero land in the middle of a tropical jungle. He’s sweaty already, dirty, and ready to leap into action to show off his survival skills to the camera. If he tells you that finding food first is a priority, you know he is full of it. While having a food source available is immensely important in the long run, it is far from your most pressing need. Humans can live up to six weeks without eating any food and that will give you plenty of time to work out more pressing issues like warmth, water, and shelter. Before you grab a cheap ticket to your survival destination, understand that food isn’t your largest priority.

I’ve always felt that hunger pains were more of a suggestion than a demand, and that’s why I often ignore them for hours at a time, sometimes. But six weeks is a long time! I would think you’d be getting pretty weak after just a couple of weeks without food. At what point would you be too weak to hunt or forage?